1. Technical Field
The present invention relates to an image reading apparatus for optically reading an original image on a platen, and more specifically, to improvements in a lock mechanism of an optical carriage for scanning the original image.
2. Description of the Related Art
Generally, this type of image reading apparatus is widely known as an apparatus such as a copier, facsimile and scanner for scanning an image original set on a read platen in a predetermined direction to convert into electric signals by a photoelectric sensor. Therefore, platen glass is disposed in an external casing, and a reading carriage is equipped to be movable along the platen, and is installed with a light-source lamp for emitting light to an original image on the platen, and reflecting mirrors for guiding reflected light from the original image to a photoelectric conversion sensor. Then, the read light from the reflecting mirror is condensed to the photoelectric conversion sensor by a condenser, lens for image formation, and such a structure is known.
Then, as an optical carriage traveling in the (sub) scanning direction along the platen, there are known a structure where the carriage is installed with a light-source lamp and reflecting mirrors, and on the apparatus frame (for example, bottom chassis) side are disposed an image-formation lens for condensing light from the reflecting mirror, and the photoelectric conversion sensor, another structure where the carriage is installed with the image-formation lens and the photoelectric conversion sensor together with the light-source lamp and reflecting mirrors, still another structure where one of first and second optical carriages is installed with the light-source lamp and reflecting mirrors, and the other carriage is installed with the image-formation lens and the photoelectric conversion sensor, etc.
In any one of the structures, the optical carriage is supported in the apparatus frame to be movable in the sub-scanning direction by a rail member, and in the apparatus frame is disposed a carriage motor for causing the carriage to reciprocate at a predetermined velocity. In the optical carriage supported to be movable in the sub-scanning direction, there is the fear that the carriage moves and that a constituent component is broken in the apparatus transport process. To prevent the accident by movement of the carriage, a method is adopted of fixing the carriage by packing in order for the carriage not to move accidentally in packing the apparatus.
Japanese Patent Gazette No. 3933282 proposes a locking mechanism for fixing an optical carriage. In the Document, an apparatus frame is provided with a lock plate to be movable between a lock position and a lock release position, the front end of the lock plate is fitted into a slit provided in a carriage frame, and the carriage is thereby prevented from moving in the sub-scanning direction. Further, in the Document, part of the lock plate is configured to cover a connector in which a power supply cord is installed, and the lock plate is configured to engage in the carriage to lock in the lock position, while inhibiting installation of the power supply cord. Then, the apparatus is proposed that installation of the power supply cord is permitted concurrently with releasing the lock of the carriage in the release position.
As described above, it is proposed in above-mentioned Japanese Patent Gazette No. 3933282, etc. to provide the lock mechanism in the optical carriage supported in the apparatus frame to be able to reciprocate. This is because such an accident may occur that the optical carriage gets out of balance and falls when moving accidentally in storing the apparatus in a packing case to carry, or moving the portable apparatus when necessary by a user. Concurrently therewith, when the optical carriage vigorously collides with the apparatus internal wall, a constituent component mounted on the carriage is broken or displaced, and may result in a cause of apparatus failure.
Therefore, conventionally, as disclosed in above-mentioned Japanese Patent Gazette No. 3933282, it has been attempted to provide the apparatus frame with the lock plate, move the plate member to a locking attitude, and fix the carriage. In other words, the carriage is fixed in a predetermined attitude by coupling the carriage and the external frame with the lock plate.
Then, such a structure has conventionally been adopted that the lock plate and carriage are coupled by fitting a fit protrusion formed in one of them into a slit groove formed in the other one, and that the carriage is inhibited from moving in the sub-scanning direction by the coupling of them. In the structure where the carriage is fixed by fitting and coupling two members, the following problem arises.
As a first problem, an operator moves the carriage to a lock position by hand, and while holding the carriage in this position, moves the lock plate to a lock position from a release position, and therefore, the lock engage portion requires a relatively large clearance. The clearance causes the carriage to vibrate intensely when undergoing shock during transport. When the vibration is repeated, the repetition results in breakage of a constituent component mounted on the carriage.
Similarly, when the vibration is repeated, failure such as wearing and rattling occurs in a convey mechanism between the carriage and a carriage driving portion. For example, in the case of the mechanism that the carriage reciprocates by driving wire, when feeble vibration is repeated, a defect occurs in winding the wire, and causes fluctuations in traveling of the carriage.
As a second problem, in the case of the apparatus configuration applying the structure where the carriage is mounted and supported in the flat-shaped rail, even when the movement in the sub-scanning direction is inhibited by the lock plate, the movement in the mount vertical direction perpendicular to the sub-scanning direction is free, and a problem occurs that the carriage floats from the mount rail. This floating is caused by the clearance between the lock plate and carriage, and is an inevitable problem in the conventional lock mechanism.
The inventor of the invention reached the idea that a biasing force is applied to the carriage to increase friction with the rail member in restricting movements in the sub-scanning direction of the carriage by the fit lock structure, and that the carriage is thereby inhibited from floating from the rail, and concurrently, is fixed by the friction acting on the carriage and rail.
It is a main object of the invention to provide an image reading apparatus for enabling an optical carriage movably supported in a rail member to be locked reliably in a predetermined position of an apparatus frame without causing failure by shock in transport.
Further, it is another object of the invention to provide an image reading apparatus for providing easy operation for locking the optical carriage in a predetermined position, and further providing a simplified and inexpensive structure for the easy operation.